Pumps come in many forms, including, for example, rotodynamic pumps, sometimes referred to as “centrifugal pumps,” and positive-displacement pumps. Some positive-displacement pumps include one or more pistons configured to displace materials including fluid such as air, liquid, and/or materials including a combination of fluid, semi-solid materials, and solid materials, such as, for example, sludge. In such pumps, in order to improve operation it may be desirable provide a relatively close fit between the one or more pistons and the housing in which the one or more pistons move. However, providing a relatively close fit may result in drawbacks relating to wear and galling of the one or more pistons and/or the housing.
For example, a positive-displacement, rotary pump having circumferential pistons may be used to pump liquid having therein semi-solid and solid material. In such pumps, providing a relatively close fit between the outer surfaces of the pistons and the pump housing may provide several potential advantages. For example, a relatively close fit may prevent semi-solids and solids from accumulating between the outer surface of the pistons and the pump housing, thereby preventing pump damage. In addition, a relatively close fit may facilitate higher pump pressure by providing a close fit along a sealing line between the piston outer surface and the housing. In addition, a relatively close fit may result in the pump being self-priming.
However, a relatively close fit between the pistons and the housing may result in, for example, galling of the surfaces of the pistons and/or housing. One potential solution to this possible drawback would be to form the pistons from non-galling materials. However, such materials may be expensive. Further, such materials may wear relatively rapidly in abrasive applications.
Therefore, it may be desirable to provide a piston for pumps that may mitigate or solve one or more of the above-noted potential drawbacks.